The metal cutting work by a machine tool produces a large volume of metal scraps, which are useful enough to be recovered for recycling. However, the metal scraps resulting from the cutting work have a variety of shapes and sizes, such as of ribbons, spirals, coils, volutes, frizz, curls, and scraps. It is cumbersome to handle such metal scraps as they are. Hence, the metal scraps are compacted into a mass of a predetermined shape by means of a compressor.
Such a metal scrap compressor generally has a structure where the metal scraps are fed into a hopper, which delivers the metal scraps to a pressure forming chamber in which the metal scraps are compression formed by a press cylinder device driven by a hydraulic pump motor unit, and where a formed article resulting from the pressure forming is discharged to the outside of the forming chamber by driving a discharge cylinder device.
It is noted, however, that the metal scraps vary in shape and size as well as in bulk density. In the case of curled metal scraps having low bulk density, for example, the metal scraps need be subjected to adjustment before pressure forming. In this connection, there is known a metal scrap compressor in which the hopper incorporates therein a shredder for finely shredding the metal scraps before delivery to the forming chamber (see, Patent Literature 1). Some metal scrap compressor may further include a mixer for preventing the degradation of work efficiency due to bridge-like accumulation of the metal scraps above there. Further, a vertical-type compressor which has a press cylinder device vertically driven is predominant because the vertical-type compressor requires less area for installation than a horizontal-type compressor which has a press cylinder device horizontally or laterally driven.
Specific operations of such a metal scrap compressor are as illustrated in fragmentary sectional views of FIGS. 2A to 2D. When the compressor is automatically started in response to a command from a controller 30, a charging step is first started. A motor M drives a screw conveyor C to rotate so that metal scraps 50 stored in a hopper 6 are charged in a pressure forming chamber 25 through a charging opening F, as being finely shredded. The charging opening is formed at an upper part of one lateral side of the pressure forming chamber. In this step, as shown in FIG. 2A, a discharge gate 12 is closed with a distal end of a discharge plunger 11 of a gate cylinder device 10 horizontally driven. The discharge gate is disposed at a lower end of the other lateral side of the pressure forming chamber 25 and is communicated with a discharge port 13 for discharging the formed article after compression forming.
Subsequently, the pressure forming step is started. The controller controls the drive of working oil pressure for a press cylinder device 20 via the hydraulic power unit. A press ram 24 at a distal end of a piston rod 23 is lowered in the pressure forming chamber 25 so that the metal scraps 50 charged therein are pressure formed into a mass. As shown in FIG. 2B, in a state in which the plunger so extended on a bottom of the pressure forming chamber as to close the discharge gate 12 with the distal end thereof, the pressure forming step is performed on the discharge plunger 11 of the gate cylinder device 10.
After the pressure forming of the metal scraps, a discharging step is started. The controller controls the drive of working oil pressure via a hydraulic power unit so that an opening operation of the gate cylinder device 10 is started so move back the discharge plunger 11. When the discharge plunger 11 is moved back to place the gate cylinder device 10 in an open state, the drive of the gate cylinder device 10 is disabled. At this time, a formed article 51 is allowed to fall to a bottom of the pressure forming chamber 25.
Subsequently, the press cylinder device 2 is driven again so that the piston rod 23 and the press ram 24 are lowered to apply final pressing to the formed article 51 fallen to the bottom, as shown in FIG. 2C. Thus, the formed article 51 is further compressed to such a thickness as to pass through the discharge gate 12 smoothly.
When the final pressing of the metal chip mass is completed, the piston rod 23 of the press cylinder device 20 is elevated together with the press ram 24. Subsequently, the gate cylinder device 10 is driven to move the discharge plunger forward. At the time when the discharge plunger 11 is moved forward to bring the distal end thereof to a position to close the discharge gate 12, the formed article 51 is discharged through the discharge gate 12 to the outside of the pressure forming chamber 25 (to the discharge port 13), as shown in FIG. 2D. The drive of the gate cylinder device 10 is disabled to complete the discharging step.
As just described, when the discharge of the formed article 51 and the return of the press cylinder device 20 are completed, the operation can proceed to the next charging step. Thereafter, the cycle of the process from the charging step to the discharging step through the pressure forming step is repeated. Since the formed articles 51 are continuously discharged to the discharge port 13 side by the repeated cycles, the preceding formed article 51 is extruded by the subsequent formed article 51 so that the formed articles discharged to the outside of the compressor successively.
In the conventional metal scrap compressor performing the above-described operations, the largest drive mechanism is the press cylinder device. A conventional structure of this press cylinder device is shown in FIG. 3. An end of a cylinder tube 21 is fixed to a cylinder flange 22. A hollow block 28 is interposed between the cylinder flange and a base 14 a top side of which includes a bottom surface of the pressure forming chamber 25. The cylinder flange and the base are coupled together by a tie rod 27. A piston rod 23 and a press ram 24 fixed thereto are moved up and down in this block 28. The metal scraps charged in the pressure forming chamber 25 disposed in a lower part of the block 28 are pressure formed by a die 26 replaceably mounted to a distal end of the press ram 24.